Available as standards for recording formats for DVD (Digital Versatile Disk) are DVD-Video, and DVD-Video Recording (DVD-VR). In each of the recording formats, a video stream encoded in accordance with MPEG (Moving Picture Experts Group), an audio stream, and sub-picture data such as subtitle data are multiplexed in accordance with MPEG 2 system. An AV (Audio Visual) stream of MPEG 2-PS (Program Stream) data is generated and the generated AV stream is recorded on a DVD.
In each of the recording formats, the recording of the AV stream onto the DVD and the reading of the AV stream from the DVD are performed on a per VOBU (Video Object Unit) basis. The VOBU contains navigation information containing control information related to reproduction and displaying of and accessing to data in the VOBU, and at least one GOP (Group of pictures). In the following discussion, it is assumed that one GOP is contained in one VOBU.
The GOP is a set of video data of at least one page contained in the video stream multiplexed into the AV stream. Editing of the video stream and random accessing of a reproducing apparatus to the video stream are performed on a per GOP unit basis. The video data herein refers to data of one frame of video stream. The reproduction time of one GOP is about 0.5 second, for example.
The video data contained in the GOP includes three types, namely, I pictures (intra-picture, intra-coded picture, and intra-frame coded picture), P pictures (predictive picture, predictive coded picture, and inter-frame forward predictive coded picture), and B pictures (bidirectionally predictive picture, and bidirectionally predictive coded picture).
The I picture is video data that has been intra-frame encoded separately from other video data (pictures). The I picture can be decoded without the other video data. When accessing the GOP contained in the video stream recorded on DVD, a reproducing apparatus of DVD accesses the I picture in the GOP. The reproducing apparatus accesses the I picture in the GOP to reproduce the I picture, for example, when the reproducing apparatus accesses any GOP for reproduction regardless of a predetermined reproduction order or when the reproducing apparatus reproduces intermittently the video data in the video stream during fast forward reproduction mode.
The P picture is video data that has been encoded (inter-frame forward predictive encoded) using the I picture or the P picture present in past in time axis of the video stream. To decode the P picture, the video data that has been used in encoding needs to be used. The B picture is video data that has been encoded (inter-frame bidirectionally predictive encoded) using the I picture or the P picture present in past and future in time axis of the video stream. To decode the P picture, the video data that has been used in encoding needs to be used. Each of the P picture and the B picture is encoded using a maximum of two pages of other video data.
To decode the video data contained in the GOP, values of two types of flags, namely, a closed GOP flag and a broken link flag are recorded on each GOP as information indicating whether the video data of another GOP is to be used. The closed GOP flag and the broken link flag are described below with reference to FIGS. 1 through 3.
The closed GOP flag indicates whether the video data of interest was encoded using the video data of own GOP only rather than using the video data of an immediately prior GOP. As shown in FIG. 1, a first B picture 11-1 and a second B picture 11-2 of a GOP 1-2 are encoded using an I picture 12-1 of the GOP 1-2, and the video data of the GOP 1-2 is not encoded using the video data of an immediately prior GOP 1-1. In this case, the value of the closed GOP flag of the GOP 1-2 is set to “1”.
If a first B picture 11-3 and a second B picture 11-4 of a GOP 1-4 are encoded using a P picture 13-1 of an immediately prior GOP 1-3 and an I picture 12-2 of the GOP 1-4 as shown in FIG. 2, the closed GOP flag of the GOP 1-4 has a value of “0”.
For example, if the editing of the AV stream causes a GOP 1-6 to be preceded by a GOP 1-5, which is different from the one that has been used in the encoding of the video data of the GOP 1-6, the broken link flag of the GOP 1-6 has a value “1”. When the video data of the GOP 1-6 is decoded, the video data of the immediately prior GOP 1-5 cannot be used (referenced). For example, the broken link flag set to a value “1” means that two first pictures 14-1 and 14-2 of the GOP 1-6 were encoded using the video data of a GOP that had been present before the GOP 1-5. In such a case, the reproducing apparatus cannot decode the pictures 14-1 and 14-2, and the reproduction of the pictures 14-1 and 14-2 becomes unnecessary.
To decode the video data contained in a GOP of interest, whether the video data of the immediately prior GOP is required or not is determined based on the values of the closed GOP flag and the broken link flag of the GOP of interest. If the closed GOP flag has a value of “1” as shown in FIG. 1 or if the broken link flag has a value of “1” as shown in FIG. 3, the video data of the immediately prior GOP is determined as being unnecessary. If the closed GOP flag has a value of “0” and the broken link flag has a value of “0” as shown in FIG. 2, the video data of the immediately prior GOP is determined as being necessary. When the reproduction of the AV stream is started, the reproducing apparatus determines whether the VOBU containing the immediately prior GOP needs to be read from the DVD by referencing the values of the closed GOP flag and the broken link flag at a reproduction start position.
The value of a progressive frame flag indicating which scanning method, interlace scanning method or progressive (non-interlace) method, the video data of the GOP is written with is recorded in each unit of video data of the GOP. If the video data is recorded using the progressive method, the progressive frame flag is turned on, and if the video data is recorded using interlace method, the progressive frame flag is turned off. For example, the reproducing apparatus repeatedly displays a video of the same frame during a slow reproduction mode or a pause of the video. If the video data recorded with the interlace method is displayed, the reproducing apparatus displays an upper field and a lower field, thereby displaying a flickering image. To prevent the video from flickering, the upper field and the lower field are synthesized into a video signal in an inter-field interpolation process. A field-interpolated video signal is thus output.
The DVD reproducing apparatus performs a reproduction process by selecting in accordance with reproduction speed between reproducing all video data (frames) contained in the GOP (hereinafter referred to as all-frame reproduction) and reproducing successively I pictures only contained in the GOP (hereinafter referred to as I picture reproduction).
In the DVD reproducing apparatus, a processor controlling the reproduction process assigns a counter counting the serial number starting with 0 (hereinafter referred to as a reproduction frame counter) to the video data during the reproduction process, and manages, on a per VOBU basis, the range of the count of the reproduction frame-counter of the video data contained in the VOBU. A decoder of the reproducing apparatus manages a counter counting the total number of frames of the video outwardly output (video displayed) (hereinafter referred to as an output frame counter). By retrieving the count of the output frame counter from the decoder, the processor acquires information regarding which VOBU the video data of the currently output (displayed) video is contained in.
Furthermore, in a proposed synchronization reproduction method (for example, Patent Document 1), data of moving image information compressed at a high efficiency in accordance with MPEG 1 method, and compressed audio data accompanying the moving image data are reproduced in well-synchronized state.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 7-170490